Ultra-stable very-low phase-noise signal source for very long baseline interferometry using a cryocooled sapphire oscillator

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dc.contributor.authorNand, N.
dc.contributor.authorHartnett, J.
dc.contributor.authorIvanov, E.
dc.contributor.authorSantarelli, G.
dc.date.issued2011
dc.description.abstractThe design and implementation of a novel frequency synthesizer based on low phase-noise digital dividers and a direct digital synthesizer is presented. The synthesis produces two low noise accurate tunable signals at 10 and 100 MHz. We report the measured residual phase noise and frequency stability of the syn thesizer and estimate the total frequency stability, which can be expected from the synthesizer seeded with a signal near 11.2 GHz from an ultra-stable cryocooled sapphire oscillator (cryoCSO). The synthesizer residual single-sideband phase noise, at 1-Hz offset, on 10and 100-MHz signals was -135 and -130 dBc/Hz, respectively. The frequency stability contributions of these two sig nals was σy = 9 × 10-15 and σy = 2.2 × 10-15, respectively, at 1-s integration time. The Allan deviation of the total fractional frequency noise on the 10- and 100-MHz signals derived from the synthesizer with the cry oCSO may be estimated, respectively, as σy ≈ 3.6 × 10-15 τ-1/2 + 4 × 10-16 and σy ≈ s 5.2 × 10-2 × 10-16 τ-1/2 + 3 × 10-16, respectively, for 1 ≤ τ <; 104s. We also calculate the coherence function (a figure of merit for very long baseline interferometry in radio astronomy) for observation frequencies of 100, 230, and 345 GHz, when using the cry oCSO and a hydrogen maser. The results show that the cryoCSO offers a significant advantage at frequencies above 100 GHz.
dc.description.statementofresponsibilityNitin R. Nand, John G. Hartnett, Eugene N. Ivanov, and Giorgio Santarelli
dc.identifier.citationIEEE Transactions on Microwave Theory and Techniques, 2011; 59(11):2978-2986
dc.identifier.doi10.1109/TMTT.2011.2166976
dc.identifier.issn0018-9480
dc.identifier.issn1557-9670
dc.identifier.urihttp://hdl.handle.net/2440/88055
dc.language.isoen
dc.publisherIEEE
dc.relation.granthttp://purl.org/au-research/grants/arc/LP0883292
dc.relation.granthttp://purl.org/au-research/grants/arc/LP0883292
dc.rights© 2011 IEEE
dc.source.urihttps://doi.org/10.1109/tmtt.2011.2166976
dc.subjectCryogenic sapphire oscillator (CSO)
dc.subjectfrequency stability
dc.subjectfrequency synthesizer
dc.subjectphase noise
dc.subjectvery long baseline interferometry (VLBI) coherence
dc.titleUltra-stable very-low phase-noise signal source for very long baseline interferometry using a cryocooled sapphire oscillator
dc.typeJournal article
pubs.publication-statusPublished

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